check the 'cartridge data base', available on line
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Al is right. All of the F-9 series were high output moving magnets. The styli differed in shape and materials used.
Most (but I don't think all) of the F9 cartridges used the same body (I think the F9L may have been an exception), and most were spec'd at 3.5mv. I suspect that the ad you referred to is incorrect, as original literature on the F9 series indicates 3.5mv for the F9E.
I agree with Tannat, though, that it doesn't matter. 3.5 mv vs. 5.5 mv is less than a 4db difference.
The reason I would be concerned about the specific model number within the series, though, is because that determines the stylus configuration. For example, while the F9E has an elliptical stylus, the F9P and F9D were conical(!), according to the original literature.
07-06-11: LewmHi Lew,
You're right, with the slight qualification that the exact nomenclature for what you are referring to is the "F-9E Ruby."
As you realize, an F-9E can be upgraded to an F-9E Ruby via a stylus replacement. The designation for the Ruby stylus itself is RS-9E.
I think what people are trying to tell you is that the difference between 3.5mV output and 5.5mV output is not going to make or break the match with the gain of your preamp. If your preamp works with only 3.5mV in, it will work fine with 5.5mV, and vice-versa. For that matter, it will work with any and all "normal" MM cartridges. The diff between 3.5mV and 5.5mV is less than 2 db.